BCL, NTX, SRB and their mix (PXT3003) improve myelination in DRG co-cultures. (A) and (B) PXT3003 treatment (Dose 2) of myelinating DRG co-cultures of neurons and Schwann cells derived from CMT1A transgenic rats (TG) demonstrated an increased length of MBP-positive fibres (red staining in (B)) compared to the untreated control (A). Scale bar: 56 μm. Blue staining: DAPI. (C) to (F) After 10–11 days of treatment of TG DRG co-cultures with single compounds BCL (C), NTX (D), SRB (E) or their PXT3003 (F) combination at four doses (Dose 1: 0.32 nM of BCL, 0.32 nM of NTX and 32 nM of SRB; Dose 2: 1.6 nM of BCL, 1.6 nM of NTX and 160 nM of SRB; Dose 3: 8 nM of BCL, 8 nM of NTX and 800 nM of SRB; Dose 4: 40 nM of BCL, 40 nM of NTX and 4 μM of SRB), myelination was significantly improved (featured by an increased length of MBP-stained segments). (G) The synergistic potential of PXT3003 (Dose 2: 1.6 nM of BCL, 1.6 nM of NTX and 160 nM of SRB) was displayed by an isobologram plotted from dose-effect curves of each drug. The calculated Combination Index (CI) of synergy was 0.36; Synergism is characterized by a CI < 1. Greyed surface represents the concentrations of the mixes at which CI = 1. Three independent DRG co-cultures with 6 replicates each were performed and analysed. +, *P < 0.05; ++, **P < 0.01; ***P < 0.001 vs Vehicle; ANOVA with Dunnett’s test (*) and t-test (+). Data are shown as mean + SEM. Vhc: Vehicle.